1. Field of the Invention
The present invention generally relates to hand-held measuring devices and, more particularly, to a new and improved multi-purpose measuring device adaptable for easily determining the major, minor and pitch diameters of a screw thread, the concentricity of the thread as well as whether the lead and flank angles of the thread are within acceptable limits. In addition, the present invention functions as a "GO" gage to indicate whether a screw thread will functionally assemble with its threaded mating part.
2. Description of the Prior Art
A multiplicity of separate gaging devices are currently required to adequately measure various parameters such as the actual pitch diameter, the functional pitch diameter, the concentricity, the minor diameter and the maximum diameter of an externally threaded screw member. For example, while U.S. Pat. No. 2,793,443 issued May 28, 1957 suggests a standard thread ring or "GO" gage, this device can not provide the pitch diameter, the concentricity nor even the minor diameter of the thread. In comparison, while the device suggested in U.S. Pat. No. 3,111,766 issued Nov. 26, 1963 can arguably be used to determine the pitch diameter, it can not provide the concentricity, the minor diameter nor a "GO" ring determination of the maximum thread size allowable for its mating part. Likewise, while the device suggested in U.S. Pat. No. 4,590,678 issued May 27, 1986 could arguably provide the concentricity of a screw thread if properly employed, it is believed that this device can not provide the functional pitch diameter necessary for determining allowable lead and flank angles as well as the minor diameter of the threaded screw.
In the aircraft industry it has become increasingly important to provide externally threaded screw members capable of meeting the stringent tolerances required for use in safety critical applications. Such threaded screw members are often inspected by relatively unskilled personnel, making it essential that any thread gage measuring devices be as easy to use as possible, while still providing the degree of accuracy necessary to meet required structural tolerances. Because the required gage measurements are often performed in less than ideal locations, such as adjacent to, or even on the thread cutting machinery, the ideal measuring device should be as compact as possible and preferably free from the need for any support holder or the like. For example, when currently determining the actual pitch diameter of a threaded work product, a plurality of three separate gaging wires are normally positioned on opposite sides of the newly cut screw thread. The gaging wires are hand held in place while a micrometer is simultaneously applied over the wires. It is evident that this procedure can easily lead to a user dropping and even losing one or more of the wires during the measuring operation. Alternatively, the three gaging wires may be retained against the screw thread by a support assembly or holder, possibly of a type suggested in U.S. Pat. No. 2,692,438 issued Oct. 26, 1954. In either case, the measurement procedure tends to be awkward at best and can easily lead to inaccurate measurement of the critical design parameters of the screw thread.
In an effort to overcome the present need for a wire holding device as well as a plurality of separate, often cumbersome devices for measuring the various parameters of a screw thread or the like, the present invention provides a unique gage plug assembly capable of permanently retaining gaging wires in their proper positions, without the need for any support or mechanical contrivance as required in the U.S. Pat. No. 2,692,438. Additionally, the present invention can provide such measurements as the functional pitch diameter, concentricity, major and even minor diameters of the screw thread. As a result, the present invention provides a thread gage measuring device uniquely capable of providing many of the necessary measurements required for assuring compliance with existing DoD and FAA directives for construction of aircraft safety critical threaded components. It should be understood that the present invention is in no way limited to use in the aircraft industry. Rather, the multi-purpose measuring device making up the present invention is adaptable for providing precision measurements of externally threaded screws, gears, splines and the like intended for use in almost any industry.